Computer systems generally incorporate a display monitor unit having a cathode ray tube for providing a visual representation of selected data to a user. A specific point on the display is often indicated to the user by way of a brightly illuminated cursor. In various applications, the cursor may be moved by the user to any desired point on the display, for example, to edit text files or select menu options.
In the earlier prior art, the positioning control for the cursor was typically provided by keys which were are manually depressed by the user to incrementally move the cursor across the screen. To overcome the awkwardness of pressing keys multiple times to move the cursor across the screen, other input devices were devised, such as the light pen.
The light pen is positioned with its tip pointed toward the display face of a direct view CRT display. The tip of the light pen includes an optical sensor for detecting the raster scan trace as it excites the phosphors in the face of the cathode ray tube. The timing of the detected raster scan signal is translated into positional data, which, in turn, is used by the computer software to control the position of the cursor on the screen. As the user moves the tip of the light pen across the face of the cathode ray tube, the cursor moves along with it, giving the user the direct interactive "feel" of drawing on the CRT face.
One disadvantage of the light pen is its low resolution. Prior art light pens can sense an area of the display screen only as small as a character, instead of a pixel, or picture element, so that lines drawn on a screen often appear as blobs of light. This is caused primarily by the large size of the optical sensor element compared to the small size of the pixels on the display screen, the persistence of the excited phosphor on the screen, and parallax effects caused by the thick glass of the cathode ray tube face.
The disadvantages of the light pen are overcome somewhat by cursor positioning devices such as the "mouse", the joystick, and the graphics input tablet, which provide improved resolution and ease of use. However, these alternative cursor positioning devices do not provide the direct interactive "feel" provided by light pens. Instead, the user manipulates these devices on a table top, for example, and this effects a corresponding movement of the cursor on the display screen.
Where there is a need for a large number of users to view displayed data many computer systems have been adapted to use projection monochrome monitors instead of direct view CRT displays. With this type of monitor, a video image is projected on a screen having a diagonal measurement of three to five feet. Although first used only for the display of video programming, the projection display monitor is becoming a popular computer display device for group viewing situations, such as computer training classes, executive meetings, and conferences.
The use of a projection display monitor could be greatly enhanced by a cursor control device that would provide for moving the displayed cursor, selecting items on menus, drawing on the projection screen, and calling up files and display windows, the same way a user of a does with a conventional "mouse" device. It would also be desirable if the user could interact directly with the projected image on the screen, similar to the way a light pen is used with a direct view CRT display unit. In this way, the actions of the user would be readily visable to the viewing group. It would be further desirable if the motion of the cursor could be resolved to the pixel level, making possible the writing or drawing fine lines on the screen.
According, it is an object of the present invention to provide a cursor positioning device for a projection monitor and display screen;
It is another object of the present invention to provide a cursor positioning device which allows the user to interact directly with the projected image; and
It is a further object of the present invention to provide a cursor positioning device having a high degree of resolution.